Microsoft Word - Cengel and Boles TOC _2-03-05_.doc

Chapter 15 | 783

In the absence of any heat loss to the surroundings (Q0),
the temperature of the products will reach a maximum, which
is called the adiabatic flame temperatureof the reaction.
The adiabatic flame temperature of a steady-flow combus-
tion process is determined from HprodHreactor

Taking the positive direction of heat transfer to be tothe
system, the entropy balance relation can be expressed for a
closed systemor steady-flow combustion chamberas

For an adiabatic processit reduces to

The third law of thermodynamicsstates that the entropy of
a pure crystalline substance at absolute zero temperature is
zero. The third law provides a common base for the entropy
of all substances, and the entropy values relative to this base
are called the absolute entropy. The ideal-gas tables list the
absolute entropy values over a wide range of temperatures but
at a fixed pressure of P 0 1 atm. Absolute entropy values at
other pressures Pfor any temperature Tare determined from

Sgen,adiabaticSprod
Sreact 0

a^

Qk

Tk

SgenSprod
Sreact

aNp^1 h°fh
h°^2 paNr^1 h°fh
h°^2 r

For component iof an ideal-gas mixture, this relation can be

written as

where Piis the partial pressure,yiis the mole fraction of the

component, and Pmis the total pressure of the mixture in

atmospheres.

The exergy destructionand the reversible workassociated

with a chemical reaction are determined from

and

When both the reactants and the products are at the tempera-

ture of the surroundings T 0 , the reversible work can be

expressed in terms of the Gibbs functions as

WrevaNr 1
g°f
gT 0

g° (^2) r
aNp 1 g
°fg
T 0
g
° (^2) p
WrevaNr 1 h°fh
h°
T 0
s (^2) r
aNp 1 h°fh
h°
T 0
s (^2) p
XdestroyedWrev
WactT 0 Sgen

si 1 T, Pi 2 
s°i 1 T, P 02
Ru ln
yi Pm
P 0

s 1 T, P 2 
s° 1 T, P 02
Ru ln
P
P 0
1.S. W. Angrist. Direct Energy Conversion. 4th ed. Boston:
Allyn and Bacon, 1982.
2.W. Z. Black and J. G. Hartley. Thermodynamics. New
York: Harper & Row, 1985.
3.I. Glassman. Combustion. New York: Academic Press,
1977.
4.R. Strehlow. Fundamentals of Combustion. Scranton,
PA: International Textbook Co., 1968.
5.K. Wark and D. E. Richards. Thermodynamics. 6th ed.
New York: McGraw-Hill, 1999.
REFERENCES AND SUGGESTED READINGS
PROBLEMS
Fuels and Combustion
15–1C What are the approximate chemical compositions of
gasoline, diesel fuel, and natural gas?
15–2C How does the presence of N 2 in air affect the out-
come of a combustion process?
15–3C How does the presence of moisture in air affect the
outcome of a combustion process?
15–4C What does the dew-point temperature of the product
gases represent? How is it determined?
15–5C Is the number of atoms of each element conserved
during a chemical reaction? How about the total number of
moles?
Problems designated by a “C” are concept questions, and students
are encouraged to answer them all. Problems designated by an “E”
are in English units, and the SI users can ignore them. Problems
with a CD-EES icon are solved using EES, and complete solutions
together with parametric studies are included on the enclosed DVD.
Problems with a computer-EES icon are comprehensive in nature,
and are intended to be solved with a computer, preferably using the
EES software that accompanies this text.